1. Field of the Invention
The invention relates to a process and to an apparatus for measuring the positions of centres of curvature of optical surfaces of a multi-lens optical system.
2. Description of the State of the Art
In the course of the manufacture of high-quality multi-lens optical systems the lenses have to be oriented with respect to one another with high accuracy. In order to be able to carry out such an orientation it is necessary to determine the positions of the optical surfaces metrologically. Even if during the adjustment of the lenses a check of the positioning accuracy is dispensed with, such measurements are regularly carried out at least within the scope of quality control.
A crucial geometrical quantity in connection with the surveying of multi-lens optical systems is constituted by the positions of the centres of curvature of the optical surfaces. Ideally the centres of curvature lie exactly on a common reference axis which, as a rule, should coincide with the axes of symmetry of the lens mounts receiving the lenses. In real optical systems, however, in consequence of tolerances of manufacturing and assembly the centres of curvature are randomly distributed around this reference axis. If the spacings of the centres of curvature from the reference axis are too great, the imaging properties of the optical system deteriorate in intolerable manner.
A process for measuring centres of curvature of optical surfaces of a multi-lens optical system is known from DE 10 2004 029 735 A1. In this process the positions of the centres of curvature of the individual optical surfaces are measured successively with the aid of an autocollimator. The first surface for which the position of the centre of curvature is surveyed is that surface which is situated nearest to the autocollimator. As soon as the position of the centre of curvature of this first surface has been determined, the following, second surface is surveyed. However, the first surface influences the surveying of the second surface. For this reason, the optical effect of the first surface has to be taken into consideration computationally in the determination of the position of the centre of curvature of the second surface. In the consideration of the optical effect of the first surface the design data of the first surface are fallen back upon, and in particular the desired radius of curvature and the desired spacing with respect to the second surface (i.e. the centre thickness of the first lens). In addition, the previously measured position of the centre of curvature of the first surface is taken into consideration computationally.
The manner of proceeding is the same for all further surfaces. In the course of the computational evaluation the measured positions of the centres of curvature of all optical surfaces situated ahead, and otherwise the design data, are consequently always taken into consideration.